I'm using zimbra since 2 weeks. I'm actually in discovering mode

Since 2 weeks the default language of the admin panel was French. Today, I've done
a reload (using the key F5 of my keyboard) and the admin panel is now at 95% in english and 5% in french.

How could I force the french language in the admin panel ? Please don't tell me that I have to reinstall zimbra lol

Thanks for your helps.